1. Field of the Invention
The present invention relates to a high-density recording scanning microscope in which a beam of charged particles is finely focused to scan the surface of a sample at a high density of, at least, 8,000 scannings, and a detected signal is converted into a digital signal, so as to directly print an image of high definition, high or rich gradation and wide view. More particularly, it relates to techniques with which a very clear image of high definition, high gradation and wide view having, for example, at least 8,000 pixelsxc3x978,000 pixels and having hitherto been nonexistent, is directly printed in, for example, colors.
2. Description of the Related Art
With a scanning electron microscope, an enlarged scanning image has heretofore been observed in such a way that a sample is submitted to planar scanning while being irradiated with an electron beam which is a finely focused beam of charged particles, so as to detect secondary electrons or the likes generated on this occasion, and that the enlarged scanning image is displayed on a cathode-ray tube through brilliance modulation, that the image on the cathode-ray tube is photographed with a Polaroid film (registered trademark) or that it is photographed with a conventional film and is printed on sensitized paper.
Besides, the photographing has been done in such a way that, at a high magnifying power, focusing and astigmatism compensation are performed into a state where the image on the cathode-ray tube is substantially focused, whereupon the magnifying power is lowered.
On account of its property, the scanning electron microscope in the prior art needs to detect the secondary electrons or the likes generated when the surface of the sample is scanned using an electron-beam spot, and to display the image through the brilliance modulation of the cathode-ray tube with the detected signal. For the observation or photographing, therefore, the displaying cathode-ray tube or even the photographing cathode-ray tube of high resolution can display only a rectangular image whose resolution is about 500 through 1,600 pixels, or about 2,500 pixels at the utmost. As a result, the prior-art scanning electron microscope has such a narrow view that only the image of a very small area, for example, an area of 0.02 mmxc3x970.02 mm when the sample is scanned at scanning intervals of 0.01 xcexcm at a density of 2,000 pixelsxc3x972,000 pixels, can be recorded by one time of photographing and then observed. This has posed the problem that the troublesome job of repeatedly photographing adjacent areas so as to overlap each other, and creating an image of wide view by pasting the images of the individual areas, is required.
On the other hand, when a large area is entirely photographed, a low-density image is obtained because the number of scanning lines is as small as, for example, about 2,000xc3x972,000 at the utmost. This has posed the problem that, even when part of the photographed image is taken out and enlarged, the image of the fine part cannot be observed.
Further, the photographing cathode-ray tube of high resolution creates an image by exposing a film to a minute light spot luminescing when a phosphor screen coated with a fluorescent material is scanned with an electron beam. This has posed the problem that the image is usually a monochromatic one, the gradation of which is too narrow to expose the film to a large number of gradation levels, for example, gradation levels of 12 bits and to print the gradation levels on sensitized paper.
In order to solve the problems stated above, the present invention has its object to provide a high-density recording scanning microscope in which a beam of charged particles finely focused scans the surface of a sample at a high density of, at least, 8,000 scannings, a signal thus detected is converted into a digital signal, and the digital signal is used for directly printing an image of high definition, high gradation and wide view, particularly a very clear image of high definition, high gradation and wide view having at least 8,000 pixelsxc3x978,000 pixels and having hitherto been nonexistent.
According to the present invention, the surface of a sample is scanned with a spot of charged particles focused by an objective lens, at a high density of, at least, 8,000 scannings for printing, and it is scanned in a direction substantially orthogonal to the direction of the first-mentioned scanning, at the high density of, at least, 8,000 scannings, or the sample surface is scanned with the number of scannings at a low density for displaying, the number of scannings being smaller than in the high-density printing, and it is scanned in a direction substantially orthogonal to the direction of the low-density scanning, with the number of scannings at the low density, a signal generated or absorbed by the scanning is detected, the signal detected at the high density is converted into a digital signal, and printing is done on the basis of the converted digital signal, or the displaying is done on the basis of the signal detected at the low density.
Herein, during the high-density scanning, the size of the spot is made substantially equal to or somewhat smaller than a scanning interval at the high density by the objective lens or a dynamic focusing coil separately disposed.
Besides, the converted digital signal is stored in a memory, and the printing is done on the basis of the digital signal read out of the memory.
In addition, the detected signal is converted into a digital color signal.
Further, a table in which color gradation levels corresponding to the gradation levels of the detected signal are registered is comprised, and the detected signal is converted into a color signal by reference to the table.
Still further, in converting the detected signal into a color signal, the detected signal is converted into the gradation level of the color signal corresponding to that of the detected signal, on the basis of two designated colors.
Yet further, the detected signal is set at, at least, 8 bits, and when the color signal consists of R, G and B signals, each of them is composed of 8 bits, or when the color signal is for the printing, the color signal has colors in a color data format for use in the printer, and the number of bits of the colors.